I replaced my ac pulley this past summer. There is a bearing in the pulley that goes bad, Continuing to drive it will eventually cause the bearing to lock up or disintegrate probably breaking your serpentine belt. I found a pulley on amazon. Get the numbers/name/model number off the side of the compressor. Search amazon, get the whole kit I think it's about $60.
Remove the front right tire and the inner fender liner. The compressor will be right in front of you, take off the center nut a 10 or 12 mm I think, there is a snap ring down in there, remove that. You'll need long jaw snap ring pliers (home depot, lowes, amazon, autozone etc) Tap the clutch with a rubber mallet till it moves and wiggle it off. Reinstall in reverse order making sure the snap ring is fully seated. Fairly simple. If your ac compressor won't engage this is a likely culprit, dealers and garages typically replace the entire compressor to the tune of several hundred or even a thousand or more dollars.
You do not need to open the ac system and chances are her ac just might work after your'e done.